Heat pipe and manufacturing method thereof

ABSTRACT

A heat pipe and manufacturing method thereof. A pipe is provided and shaped. A molding bar is inserted into the pipe. A wick structure is formed in the pipe. The molding bar is separated from the pipe. A working fluid is added and confined in a closed space of the pipe. The pipe is shaped before formation of the wick structure therein to prevent damage to the wick structure.

BACKGROUND

The invention relates to a heat pipe, and in particular to a heat pipeand a manufacturing method thereof.

In the continued development of electronic devices, the number oftransistors per unit area in an electronic device has increased toimprove performance. As working efficiency is increased, frequentturning on or off of the transistors causes switch loss, increasing thetemperature of the electronic device. In recent years, as development ofsemiconductors and IC design has improved, chip speed has substantiallyincreased. Consequently, during operation of chips, heat energy isproduced due to increases in clock frequency. Higher temperatures,however, lower chip speed such that performance deteriorates, andlifetime of the chip may be reduced accordingly.

External fans and heat-dissipation devices are normally installed inelectronic devices to dissipate excess heat and maintain workingtemperature. Since heat dissipation of the electronic devices canincrease effective chip speeds, fan speed is increased to accelerateheat conduction. However, power consumption and noise level bothincrease accordingly. As well, heat-dissipation devices such asheat-dissipation fins, while improving heat conduction, reduce theavailable internal space. Thus, currently, a heat pipe with a smallcross section and low temperature differential is often used to providea relatively long distance for heat conduction without requiringadditional power supply. Further, compared to the heat-dissipation fins,the heat pipe occupies less internal space, and thus, is widely used inelectronic devices.

FIG. 1 is a flowchart showing a conventional manufacturing method of aheat pipe. In step 102, a hollow copper pipe with a sealed end isprovided. In step 104, a bar is inserted in the pipe. Since the pipe hasa sealed end, normally being outwardly protruding and conical, an end ofthe bar can be disposed on the top of the conical sealed end. A gap isthus maintained between an inner wall of the pipe and the bar. Thematerial of the bar is stainless steel, graphite, or other rigidmaterials.

In step 106, copper powder is filled in the gap between the inner wallof the pipe and the bar. Additionally, the copper powder can be furthercompressed and densely compacted according to the needs ofmanufacturers. In step 108, the copper powder is sintered to form a wickstructure (or capillary structure) on the inner wall of the pipe. Instep 110, the bar is pulled out from the pipe. In step 112, a workingfluid is added, the pipe is vacuumed and the pipe opening is sealed.Depending on different wick structures, the steps of adding workingfluid and vacuuming can be interchanged. In step 114, the completedcylindrical heat pipe is bent and pressed flat, with the final shapethereof depending on the requirements of subsequent heat-dissipationmodule design.

After manufacturing, however, in practice, the heat pipe, originally astraight cylindrical pipe, is reformed to become bent or flat. A portionof the wick structures in the pipe near the bent or areas isconsequently impaired, losing heat conduction function, by as much as70% or more.

SUMMARY

Embodiments of the invention provide a manufacturing method for a heatpipe. The pipe is shaped before formation of the wick structure thereinto prevent damage to the wick structure from subsequent process, therebyretaining heat conduction ability.

The heat pipe is applicable in a heat-dissipation module of anelectronic device, being shaped according to requirements of theheat-dissipation module. In the manufacturing method, a pipe is providedand shaped. A molding bar is inserted into the pipe. A wick structure isformed in the pipe before the molding bar is separated from the pipe. Aworking fluid is added in the pipe and confined therein.

Embodiments of the invention further provide another manufacturingmethod for a heat pipe. A pipe is provided and shaped. A molding bar isinserted into the pipe. The molding bar is separated from the pipebefore a wick structure is formed. A working fluid is added in the pipeand confined therein.

The pipe can be shaped by bending or pressing flat. Further, someprotrusions are formed on a surface of the molding bar to maintain a gapbetween the inner wall of the pipe and the molding bar. The molding barand the protrusions have the same material as that of the wick structureso that the molding bar and the protrusions become one part of the wickstructure during formation. Alternatively, before separating the moldingbar from the pipe, the protrusions are heated to vaporize or liquefy.The molding bar has flexible material such that the molding bar can beeasily withdrawn from the pipe. The molding bar has a lower burningpoint than the wick structure so that the molding bar is separated fromthe pipe by being heated to vaporize or liquefy. Alternatively, themolding bar, soluble in an organic solvent, can comprise organicallysoluble material such as an organic polymer, soluble in an appropriatesolvent such as acetone, so that the molding bar is separated from thepipe by being dissolved in the organic solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description in conjunction with the examples and referencesmade to the accompanying drawings, wherein:

FIG. 1 is a flowchart showing a conventional manufacturing method of aheat pipe;

FIG. 2 is a flowchart showing a manufacturing method of a heat pipeaccording to a first embodiment of the invention; and

FIG. 3 is a flowchart showing a manufacturing method of a heat pipeaccording to a second embodiment of the invention.

DETAILED DESCRIPTION First Embodiment

FIG. 2 is a flowchart showing a manufacturing method of a heat pipe of afirst embodiment of the invention, in which, in step 202, a pipe isprovided, and the material of the pipe includes plastic, metal, alloy,or non-metal materials. In this case, a copper pipe is provided as anexample. In step 204, the pipe is shaped according to the subsequentmanufacturing requirements of a heat-dissipation module. The pipe can beshaped by bending or pressing.

In step 206, a molding bar is inserted in the pipe with a gap maintainedbetween the inner wall of the pipe and the molding bar. The molding baris a flexible material allowing easy withdrawal from the bent or pipe. Aplurality of identical-sized protrusions, formed on the surface of themolding bar, allow not only the gap between the inner wall of the pipeand the molding bar to be maintained, but also maintain constant gapsize throughout the pipe.

In step 208, copper powder is filled in the gap between the inner wallof the pipe and the molding bar. In step 210, a wick structure is formedtherein. The wick structure is preferably a mesh wick, fiber wick,sinter wick, or grooved wick, formed by sintering, gluing, filling,depositing, and so on. In this embodiment, the copper pipe is used, andthus, copper powder or other metal alloy powder is filled in the gapbetween the inner wall of the pipe and the molding bar before sinteringto form the wick structure. The copper powder can be further compressedand become densely compacted before sintering so that the wick structureof varying porosity or structure is formed. Also, different fillingmaterials may require corresponding solvent or chelating agents toincrease density of the copper powder, whereby, before sintering, dryingor removal of solvent or chelating agents may be required to remove thesolvent or chelating agents.

In step 212, the molding bar is separated from the pipe, and in step214, working fluid is added and vacuum is then performed. The pipe issealed and working fluid is confined and flows in a closed space of thesealed pipe. The working fluid can comprise inorganic compounds, water,alcohol, liquid metal such as mercury, ketone, chlorofluorocarbons(CFCs) such as HFC-134a, or other organic compounds. Generally, the mostfrequently used working fluid is water. Because the surface tensionbetween corresponding fluids differs with wick structures, the sequenceof adding the working fluid and vacuuming can be interchanged, followedby sealing the pipe.

Second Embodiment

FIG. 3 is a flowchart showing a manufacturing method of a heat pipe of asecond embodiment of the invention. The steps of the second embodimentare similar to those of the first embodiment. In step 302, a pipe isprovided, preferably a copper pipe. In step 304, the pipe is shapedaccording to the subsequent manufacturing requirements of aheat-dissipation module. The pipe can be shaped by bending or pressing.

In step 306, a molding bar is inserted in the pipe with a gap maintainedbetween the inner wall of the pipe and the molding bar. In step 308,copper powder is filled in the gap between the inner wall of the pipeand the molding bar. Additionally, according to the size of copperpowder grains and porosity of wick structure, other manufacturing stepsare implemented. For example, after filling the copper powder, thecopper powder is compressed. Different filling materials may requirecorresponding solvent or chelating agents to increase density of thecopper powder, whereby before forming the wick structure, drying orremoval of solvent or chelating agents may be required to remove thesolvent or chelating agents.

Furthermore, in step 310, the molding bar is separated from the pipe. Instep 312, a wick structure is formed. The wick structure is preferably amesh wick, fiber wick, sinter wick, grooved wick, formed by sintering,gluing, filling, or depositing, and so on. Lastly, in step 314, workingfluid is added therein and followed by vacuuming. The opening of thepipe is sealed to complete production of the heat pipe. Because thesurface tension between fluids differs with wick structures, thesequence of adding the working fluid and vacuuming can be interchanged,followed by sealing the pipe.

In the second embodiment, the molding bar is separated from the pipebefore forming the wick structure, and the steps can be interchangeddepending on different manufacturing requirements. The molding bar isflexible with a plurality of protrusions formed on a surface thereof.Furthermore, the molding bar may have a lower burning point than thewick structure. Alternatively, the molding bar may comprise a materialsoluble in organic solvents, such as an organic polymer.

Since the molding bar comprises a flexible material, the molding bar canbe easily withdrawn from the pipe. Furthermore, because a plurality ofprotrusions on the molding bar are the same material as that of the wickstructure, the protrusions are sintered and become one part of the wickstructure during formation of the wick structure. The protrusions mayalso have a lower burning point than the wick structure, such thatduring sintering the protrusions are vaporized or liquefied.

If the molding bar comprises a material soluble in an organic solvent,the molding bar is dissolved by the organic solvent. For example, whilethe organic solvent is an organic polymer, the solvent is acetone.

In conclusion, in embodiments of the invention, the pipe is shapedbefore forming the wick structure in the pipe. Since after formation ofthe wick structure there is no subsequent process of the pipe, the wickstructure can be preserved. Thus, the heat conduction ability isincreased. Furthermore, the heat pipe produced by the manufacturingmethod is applicable in any heat-dissipation module of electronicdevices. The pipe can be initially shaped according to requirements ofdifferent heat-dissipation modules so that the contact area between theheat pipe and a surface of an electronic device is maximized to increaseheat dissipation.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

1. A tie-layer adhesive composition comprising: (a) 80 to 95 weightpercent or more, based on the weight of the composition, ethylene-C₄₋₈α-olefin copolymer base resin having hard and soft phases that form anetwork structure, density of 0.925 g/cm³ or less, melt index from 0.3to 5 g/10 min and which when in the pelletized form, exhibits areduction in ER of 10 percent or more to a final ER value of 1.0 or lessupon rheometric low shear modification or solution dissolution, and (b)less than 5 weight percent, based on the weight of the composition,modified polyolefin which is an ethylene-C₃₋₈ α-olefin copolymer havinga density of 0.905 to 0.965 g/cm³ grafted with 0.5 to 2.5 weight percentethylenically unsaturated carboxylic acid or ethylenically unsaturatedcarboxylic acid derivative.
 2. The adhesive composition of claim 1having a melt index from 0.5 to 5 g/10 min and wherein the modifiedpolyolefin (b) is an ethylene-α-olefin copolymer grafted with maleicanhydride.
 3. (canceled)
 4. The adhesive composition of claim 2 wherein(a) is a copolymer of ethylene and hexene-1 having a melt index of 0.5to 2.5 g/10 min.
 5. The adhesive composition of claim 4 wherein (a) hasa density of 0.910 to 0.920 g/cm³ and melt index of 0.5 to 1.5 g/10 min.6. The adhesive composition of claim 2 wherein (b) is a grafted highdensity polyethylene copolymer having a melt index from 0.5 to 20 g/10min and density from 0.945 to 0.965 g/cm³.
 7. The adhesive compositionof claim 6 wherein (b) is grafted with 0.75 to 2.2 weight percent maleicanhydride and has a melt index from 4.5 to 8 g/10 min.
 8. The adhesivecomposition of claim 2 wherein (b) is a grafted linear low densitypolyethylene copolymer having a melt index from 0.5 to 20 g/10 min anddensity from 0.910 to 0.930 g/cm³.
 9. The adhesive composition of claim8 wherein (b) is grafted with 0.75 to 2.2 weight percent maleicanhydride and has a melt index from 4.5 to 8 g/10 min.
 10. The adhesivecomposition of claim 2 which contains 95.5 to 99.5 weight percent (a)and 0.5 to 4.5 weight percent (b).
 11. A multi-layer barrier filmcomprising a barrier resin layer wherein the barrier resin is selectedfrom the group consisting of ethylene-vinyl alcohol copolymer and nylonand adhesively bonded thereto a tie-layer adhesive compositioncomprising 80 to 95 weight percent or more, based on the weight of thecomposition, ethylene-C₄₋₈ α-olefin copolymer base resin having hard andsoft phases that form a network structure, density of 0.925 g/cm³ orless, melt index from 0.3 to 5 g/10 min., and which when in thepelletized form, exhibits a reduction in ER of 10 percent or more to afinal ER value of 1.0 or less upon rheometric low shear modification orsolution dissolution, and less than 5 weight percent, based on theweight of the composition, modified polyolefin which is an ethylene-C₃₋₈α-olefin copolymer having a density of 0.905 to 0.965 g/cm³ grafted with0.5 to 2.5 weight percent ethylenically unsaturated carboxylic acid orethylenically unsaturated carboxylic acid derivative.
 12. The barrierfilm of claim 11 produced by extrusion or coextrusion processes.
 13. Thebarrier film of claim 11 wherein the tie-layer adhesive composition hasa melt index from 0.5 to 5 g/10 min and the modified polyolefin is anethylene-α-olefin copolymer grafted with maleic anhydride.
 14. Thebarrier film of claim 13 wherein the base resin is a copolymer ofethylene and hexene-1 and has a melt index of 0.5 to 2.5 g/10 min andthe modified polyolefin is a grafted high density polyethylene copolymerhaving a melt index from 0.5 to 20 g/10 min and density from 0.945 to0.965 g/cm³.
 15. The barrier film of claim 13 wherein the base resin isa copolymer of ethylene and hexene-1 and has a melt index of 0.5 to 2.5g/10 min and the modified polyolefin is a grafted linear low densitypolyethylene copolymer having a melt index from 0.5 to 20 g/10 min anddensity from 0.910 to 0.930 g/cm³.
 16. The barrier film of claim 11wherein the tie-layer adhesive composition is adhesively bonded to bothsides of the barrier resin layer.
 17. The barrier film of claim 11comprising a further polyolefin resin layer wherein the polyolefin resinis selected from the group consisting of low density polyethylene,linear low density polyethylene, high density polyethylene,ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer,ethylene-acrylate ester copolymer, ethylene-methacrylic acid copolymer,ethylene-methacrylic ester copolymer and ionomer and wherein thetie-layer adhesive is disposed between the barrier resin layer and saidpolyoloefin resin layer.